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The present invention relates generally to internal combustion engines using thermodynamic cycles such as the Otto Cycle or Diesel Cycle, and, in particular, to rotary engines.
The internal combustion engine releases the potential energy stored in fuel, such as gasoline, by burning the fuel and providing a means to convert the gases released by combustion, which expand according to the Otto Cycle or the Diesel Cycle, into mechanical energy.
In the last century, the means by which the gas expansion force has been converted into mechanical energy has been the focus of much development and refinement. Traditional engine designs have concentrated on the reciprocating engine that allows the expanding gas to act on the rotating element such as a shaft indirectly through a piston and rod. As the gas expands, pressure is exerted on a piston in a cylinder and the piston is forced downward. A rod attached to the piston transmits the downward force to a crankshaft. The force acts tangential to the rotation of the shaft and creates a torque on the shaft. In response to the torque applied to the shaft, the shaft begins to turn. While this arrangement is a venerable one, it has shortcomings due to large mass to low power ratio, high friction due to many moving parts, low relative speed, and high cost due to complexity of the assembly.
These shortcomings have pushed inventors toward developing rotary engines where the expanding gas is applied directly to the rotating element that produces mechanical energy instead of through pistons, rods, and crankshafts. A rotary engine typically has a rotor that turns inside a housing, and is either directly connected to a shaft, which is analogous to the crankshaft in a reciprocating engine, or is connected to a shaft through a planetary gear system. Many practical rotary designs have used a specially-shaped cavity inside a housing and a gear system to allow the rotor to follow the contours of the cavity to achieve the expansion and compression phases of the Otto Cycle. The planetary gear rotary engine is also proven and refined, but it has several limitations such as epitrochoidal housing shapes requiring complicated machining and rotor seals.
Simpler rotary engine geometries exist including engines employing oval-shaped interior housing cavities. The oval cavity shape allows direct attachment of the rotor to the shaft, thereby eliminating the planetary gears and increasing the efficiency. The rotors are smaller and use thin vanes that respond to the oval cavity and allow for the dimensional changes of the control volume. Until now, such arrangements have relied on rotors with special slots where the vanes retract mechanically into the rotor. This system is complicated and requires additional moving parts, such as bearings, and machining steps.
Therefore, the need exists for an engine that offers (1) direct conversion of chemical energy to rotational mechanical energy (2) direct connection of the rotor to the shaft and (3) a minimum of moving and machined parts.
The present invention is a rotary engine that uses plural, resilient, flexible, equally distributed vanes fixed to a central hub, or rotor. The invention is also a vehicle with the improved rotary engine and a rotor assembly. In one application, the vehicle is a drone airplane, however, other applications such as helicopters, boats, and land-based vehicles are possible where a drive train, with a transmission and wheels, is used instead of a propeller. The essential elements of the vehicle are a frame to which the engine is mounted, a means for controlling the engine such as a servo or cable control connected to a throttling valve, and an output means such as a propeller or drive train to convert the engine output shaft work into vehicle propulsion.
The engine output shaft is connected to the rotating element of the rotary engine. In the preferred embodiment, the rotating element is a rotor, which directly turns the output shaft centered in the engine housing having an oval-shaped interior cavity surface and four equally spaced vanes. However, a stationary rotor in a rotating housing is also possible as was shown by some of the earliest inventions of Dr. Felix Wankel.
In the preferred embodiment, the oval housing cavity shape causes the distance between the interior surface of the housing cavity and the shaft center at the nearest point to vary cyclically as the shaft and rotor turn. The resilience and flexibility of the vanes allows for bending of the vanes as the shaft rotates while the vanes resiliently adapt to the cyclical variation in the radial distance between the interior surface of the housing cavity and shaft center. The vanes bend away from the direction of rotation. Contoured recesses in the rotor receive the vanes, anchoring them so they do not separate from the rotor and allowing the vanes to flex in cooperation with the housing. The cooperation between the vanes and the housing is such that the vanes form a movable seal with the housing interior surfaces and define a number of chambers equal to the number of vanes. The cyclical variation in distance changes the volume of each chamber cyclically to accomplish the four-phase internal combustion cycle approximating the Otto Cycle.
The four phases of engine operation are:
(1) Intakexe2x80x94rotating vanes sweep an expanding fluid, such as an air-fuel vapor mixture, into the engine through an intake port in the housing. The air-fuel vapor mixture is delivered through carburetors or various fuel injection arrangements typical of combustion engines.
(2) Compressionxe2x80x94the expanding fluid is compressed. The vanes move the expanding fluid in orbit around the hub so that the chamber volume decreases, the vanes bending in reaction to a decreasing radial distance between the rotor and the interior surface of the housing cavity.
(3) Combustion/Expansionxe2x80x94at maximum compression, an expansion-initiating means such as a spark plug, glow plug, or compression ignition ignites the air/fuel mixture. The expansion initiating means can be simply a threaded hole or an entire pre-combustion chamber with multiple spark plugs. The resulting combustion causes the compressed mixture to combust which in turn causes the products of combustion, namely gases, to expand, causing a force to be applied to the vanes. The applied force creates a torque on the rotor and shaft. Power is transmitted through the shaft to perform work.
(4) Exhaustxe2x80x94the expanding fluid has fully expanded and combustion has been fully accomplished. Residual gases are swept along by the vanes to an exhaust port and are vented to the atmosphere.
In the preferred embodiment, gasoline will be used as a fuel and a spark plug will be used as the expansion initiating means. However, any number of conventional fuels may be used including hydrogen, methane, alcohol, propane, and diesel fuel. It is foreseeable that such other fuels may require changes to the expansion initiating means as well, including a pre-combustion chamber to obtain a more complete combustion of leaner fuel mixtures.
Housings and rotors made of other materials besides metal, such as thermoplastics, are also possible, as are parts coated with friction reducing compounds. Lightweight materials would complement the rotary engine""s benefits of high power to weight ratio and simplicity. The low friction components would also complement the rotary engine""s efficiency.
It is also conceived that the engine could operate using other thermodynamic cycles such as the Diesel Cycle, or as a pump as the expansion initiating means could be a tube that would supply high-pressure fluid to the expansion chamber.